While classical X-ray imaging measures absorption of X-rays caused by an object, phase contrast imaging aims at a detection of a phase shift X-rays are subjected to when they pass through an object to be examined. For phase contrast imaging and/or dark-field imaging, an interferometer (e.g. a grating) is placed behind the object to generate an interference pattern of intensity maxima and minima when the object is irradiated with (coherent) X-rays. Any phase shift in the X-ray waves that is introduced by the object causes some characteristic displacement in the interference pattern. Measuring these displacements therefore allows reconstructing the phase shift of the object. In addition, when employing such interferometer, the generation of image data deriving from de-coherent X-ray small angle scattering is enabled. The latter type of imaging is also referred to as “dark-field imaging”.
A grating based phase contrast computed tomography scanner for medical applications comprises a plurality of detector tiles. Each detector tile comprises an interferometer and a radiation detector element. Such a detector may also be called a tiled detector.
Tiling, however, implies that there may be gaps between adjacent tiles. In particular, in case of phase contrast CT systems, the tiling may be a challenge to image quality, at least for two reasons: Firstly, if differential data are acquired the interpolation of data across gaps between tiles may be even more critical than for standard, non-differential data. Secondly, each tile may comprise two gratings and a radiation detector and has a depth of a couple of centimeters, which is defined by the Talbot distance of the interferometer. This condition may increase the gaps even further.
U.S. Pat. No. 5,164,973 A1 describes a projection detecting apparatus for computed tomography, which includes a tiled detector.